A wide thought distribution about grinding

There’s a number of various grinding-related thoughts rolling around my head at the moment. They’re not fully formed (and possibly red-herrings, so look out!) but I thought I should put them out there. I don’t have any data to back them up, and I’m even sure they’re all true.

As such, this will be a slightly more conversational and open-ended post compared to most of my writings of last year, and I hope many of you can engage with it in the comments below or in the Slack.

1. Fines are Fine

Fines are the tiniest of coffee grinds. I’ve been hearing more and more professionals calling any coffee grind smaller than ~100 microns (0.1mm) in diameter a fine and I’m inclined to agree. They’re the ones that get stuck in your pores, and lend your shoes that unmistakable eau de barista after a shift.

Fines have have a lot of surface area, and not a lot of volume. This means that all of their coffee flavour is pretty much instantly accessible to water. Compare this to a large coffee grind (a boulder) where the vast majority of the flavour is hidden away inside the grind and you’ll quickly see why grind size is such a big deal. For more information on this, head to my early post ‘Surface Area and Time’.

For as long as fines have had a name, it seems like people thought they were evil. “Fines instantly over-extract making your brew taste terrible” being the most common phrase I’ve heard over the years. I’m now fairly certain that’s untrue, and I can’t help but think the complete opposite is more likely.

In 2013 I went to Mahlkonig and ran some tests on the EK43 to figure out why it makes coffee taste so delightful. Turns out it produces many more fines than any of the other grinders in the test at comparable settings. So, best-in-category grinder produces more of the ‘evil’ stuff than any of the others. This was a red flag that kick started my hunt for more answers.

When sifting my coffee for the 2012 World Brewers Cup, I was eliminating all grinds below 250 microns. I had to then lengthen the brew time and increase my extraction to levels higher than I’d ever seen before (+25%). This ultra-high extraction tasted super great, and is very similar to the level of extraction that every fine undergoes during every brew; maximum. Nearly-maximum extraction tasted so good I managed to take home the title. So why do fines get blamed for bad over-extracted flavours when over-extracted but sifted coffees taste great?

Posit: Perhaps temperature/time/roasting is to blame for over-extraction, not fines.

Nearly every brew ever made has had fines in it. And if you think about it, the outer surface of the larger grinds should behave exactly the same as the fines themselves (It’s the inside of the larger grinds that creates the problems). This means that a whole lot of the dissolved coffee flavour has come from “fine-like” extractions. Perhaps, once the roast is of good quality, it’s brew time and temperature that are coaxing out undesirable flavours of over-extraction.

2. Alignment is Key

Grinding burrs need to be parallel, and concentrically and radially aligned to work properly. The tolerances required are miniscule. A misalignment of ~0.05mm noticeably changes the quality of coffee produced by a grinder.

A number of baristas have been experimenting with alignment of their burrs and seeing extraordinary results. Ever since I played around with a Versalab grinder and saw how bad the coffee tasted when the burrs were misaligned, I’ve been very conscious about alignment. Frank at Titus Grinding (@titusgrinding on instagram) has been doing lots of cool things with the Versalab grinder; improving their alignment and surface finishes.

EK43’s have a little bit of play between the burrs and carrier/body. This can lead to misalignment if assembled without care. EK43’s that are aligned well make coffee that’s blindingly obviously better. (I’m currently working on a visual guide for proper alignment, and thinking of building a kit to align the burrs during assembly. Please let me know if you’re keen to buy a jig that does that.)

Alignment is one of those things that’s (kind of) free, and can make a massive difference to coffee quality. I often say VST baskets are the best bang-for-buck improvement you can make to your coffee. I’m feeling like proper burr alignment could be next on the list.

3. Boulders Might Just Be Structural

Lots of Baristas are frustrated with the non-linear relationship between grind size and extraction in espresso. eg. Medium grind = low extraction, Fine grind = high extraction, Finest grind = low extraction. It is assumed that this effect is caused by the grinds becoming so fine that they form pockets impervious to water flow, causing micro-channeling and a lower extraction.Maybe the larger grinds are also there to provide a structural matrix that prevents the smaller grinds from gumming everything up? I’d be keen to see/do an experiment where fines are mixed amongst larger insoluble particles to see if this carries any weight.

4. Bean Temperature Matters

I’ve been involved in a soon-to-be-published paper on grinding alongside many others. Christopher Hendon and Maxwell Colonna-Dashwood (the authors of Water for Coffee) were the primary masterminds for it, and I’m confident we’ll shed some light on this situation.Once published, I’ll be posting a version of the paper in regular human English. The ramifications for grinding tech are super interesting.

Is there anything grinding-related that’s got you thinking? Do any of these points seem ridiculous? Hit me up below

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I really like the points you’ve brought up here. I think that the future of advancements in coffee brewing (especially espresso) will revolve around increased knowledge and functionality of grinders. To your 3rd point, I think the reason very fine grounds extract less is a combination of two things: 1) the massive amount of surface area that causes water to immediately become saturated with dissolved solids to the point of being a less effective solvent, and 2) your point about hydrodynamic dispersion happening less effectively because of clumping caused by static electricity. I’ve also noticed another phenomena that only occurs… Read more »

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2 years ago

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Chris G

Hi Matt,

so if I understand you correctly on point 1.
Fines are good thing, BUT only if the distribution of all the particles are of similar size?

Just curious if you did any testing and what your experiences have been with the mahlkonig Peak grinder.

thanks

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2 years ago

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Dalton Greene

Nice post, I’d certainly buy equipment that would aid with burr alignment. I take a lot of care when cleaning/replacing and I am always unsure if it was aligned right, really don’t need more variables to mess up.

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2 years ago

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James

Matt I’m interested in an issue relevant to a lot of home baristas; the implications of single dosing grinders and what effect, if any, this has on extraction vs. a dose ground with a fully loaded hopper. When single dosing you seem to get 3 distinct phases of grind: a) initial up-take of beans into the burrs where there is nothing blocking the passage of the grounds of the burrs and there are beans above the burrs pushing down b) mid-grind where there are grounds in front of the beans and beans behind the burrs c) the end phase where… Read more »

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2 years ago

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Jose Pereyra

I have had my encore for about the same amount of time. My only problem with it is that the flanges on the upper burr break fairly easy(I’ve had to replace the plastic twice) If you notice a lot of chaff or inconsistent grind, make sure the flanges aren’t damaged. You can get replacement burrs or just the plastic burr holder for pretty cheap(no more than 15USD) off the Baratza website. Plenty of YouTube vids on how to refurbish, recalibrate and replace out there as well.

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2 years ago

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James

Well he mentions parallel alignment, concentric and radial. Not sure the difference between concentric and radial. Unless he is referring to run-off of the drive shaft causing the burr to not run ‘true’. Is that what you mean by Nutation?

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2 years ago

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knudi68

Pros and cons with the baratza encore? Pr now I have Wilfa WSCG-2 grinder which a budget grinder from Norway that Norwegian barista Tim Wendelboe recommend as an entry-level grinder . It cost approximately 50 EUR . It grinds pretty even , except if I am grinding coarse for chemex. I use it for chemex, v60, aeropress and kalita wave 185 . It’s my second one and fairly pleased but now the burrs isn’t sharp enough anymore. I’ve had it for 2 years. I can get baratza encore for approximately 150EUR.. I won’t go much than 150 EUR on a… Read more »

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2 years ago

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ericbusby

I was thinking this when I was grinding coffee for a pour over the other day and would definitely be interested in any replies to this.

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2 years ago

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ricardo mesa

Hi Matt, It makes perfect sense to me that fines are definitely not a problem, nor are boulders for that matter. The problem is consistency in grind size, t

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2 years ago

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Nickerss

I’d definitely be interested in buying an EK43 alignment jig!

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2 years ago

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Édouard Fabi

When you talk about alignement, is it as important with conical burrs as it is with flat? How would you proceed to align conical burrs? I recently bought a Compak F10 with 68mm conical, which I like very much so far, and I’m curious to know if my burrs are well aligned and if not, to see the difference once I’ve aligned them. And I might also ask, would you say flat is better than conical for espresso? If so, why? And btw, thanks again Matt for the article, it answered a few questions I had and opened up new… Read more »

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2 years ago

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mattymooners

On the issue of fines, does the following theory seem plausible… ? When making a brew with a mixture of fines and boulders, the fines extract more “fully” yet the boulders extract from the outside leaving the centre under-extracted. This means that your effective dose is lower than you think because a portion of your dose is not very accessible to the water. It follows that brewing with a low dose makes it easy to over-extract. Contrast this to a mixture that is higher in fines with not many boulders. Your “effective” dose is now higher as more of it… Read more »

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2 years ago

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knudi68

I had the same flange problem with my first wilfa cgr grinder, but it is not possible to get spare parts from them. Thanks for the tip, I’ll keep that in mind. I will probably go for Baratza encore. Anyone who knows how Rancilio rocky is in grind consistency compared to Baratza encore. Not for espresso, but for chemex, v60 and aeropress?

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2 years ago

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dsc

Matt, I’m interested in proof behind the following statement: “A misalignment of ~0.05mm noticeably changes the quality of coffee produced by a grinder. ” What testing has been done to arrive at the ~0.05mm value of misalignment? also what is “~” in terms of mm / um? I’d much rather see a +/- value rather than something which looks a bit like a finger in the air value. 0.05mm is fairly hard to achieve on any grinder in terms of runout for example, although it’s not a huge value when compared against the actual burr gap, at least on conicals.… Read more »

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2 years ago

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Philipp

+1

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2 years ago

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dsc

Yes conical burrset need to be aligned as well, the issue is that pretty much all currently available grinders are pretty hard / impossible to align yourself. I’d say there’s two ways to align conical burrsets: 1. the easy way – bring the burrs together so that they lock together, assuming the burrs are made well and clean, it should give you a fairly good alignment and concentric running. 2. the hard way – mount the outer burr loose and then use a dial indicator to indicate the inside / outside edge of the outer burr, you can tap the… Read more »

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2 years ago

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Nickerss

What grinder are you using? I had some issues single-dosing the Baratza Vario. It was very inconsistent. Sometimes it’d take 20 seconds or so for the first drops of espresso to appear, sometimes it’d take about 5 seconds on the same grind setting. This was on more or less back-to-back shots, maybe a few minutes in between, so I don’t think there were any other variables like bean temperature changing or anything like that. I like my EK43 now 🙂

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2 years ago

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dhb

Great Post Matt, I recently came across Chris Tamper Tantrum presentation which is one of my favorites so far, and looking forward to get more inside soon. Burr alignment is a hot topic on the german kaffee-Netz forum for quite awhile. No wonder you mentioned Frank.
Grinding will continue to be a area of improvement, due to stacknation of improvement in the coffeemachine field.

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2 years ago

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Lone Pine Coffee

Yes to the jig!

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2 years ago

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Matt Perger

This is pretty much impossible. Coffee grinds are brittle. Break one in half and you get thousands of tiny bits shattering off. The shattered particles are crucial for extraction, but too many of them results in an un-filterable brew.

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2 years ago

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Matt Perger

Totally. The inside of the boulders is just dragging your extraction down, while the fines and external surfaces are bringing it up. So our average is somewhere in the middle.

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2 years ago

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Matt Perger

0.05 was merely an example to show people that misalignment is important at dimensions smaller than they ever think about or deal with in day to day coffee-making.

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2 years ago

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Matt Perger

Yeah some burrs have this problem. I think it’s best to just keep things consistent with each grinder/burr set and they’ll stay the same.

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2 years ago

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dsc

So was the 0.05mm quoted simply because it’s not much in terms of dimensions, or is this backed up by real data? 0.02mm is also not much, same goes for any random number between 0 and 0.1mm I’d say, but how you achieve this kind of alignment is a different story (0.08mm is fairly easy speaking from experience, but to get down to 0.02mm you’d need some precisely made parts and good design).

T.

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2 years ago

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mattymooners

is it not that the boulders are actually causing the over-extraction as the surface area of your grinds is much lower if you have a lot of boulders? same water, lower effective dose -> over-extraction?

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2 years ago

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Matt Perger

Pretty much everything. Any misalignment has an effect.

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2 years ago

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Matt Perger

Yeah so a good way to communicate this would be with the standard deviation from the mean. Then you know how spread out everything is!

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2 years ago

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Matt Perger

As Tom said above! They’re pretty tricky. And a lot of the problems you’ll encounter are to do with the machine itself.

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2 years ago

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James

Has anyone done any testing to show what effect it has? In terms of EY% drop for example?

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2 years ago

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Nick

“While the fines and external surfaces are bringing it up”. There is surely no need to consider what you call the ‘effective dose’. Perhaps compare the sample’s extraction average (which will be calculated using the known dose mass) to the extraction of one of the sample’s constituent ‘pieces’. I would propose we consider a ‘piece’ of coffee here whose volume to surface area ratio approaches zero, and how its ‘exposure’ (determined by, amongst other things, its whereabouts; centre vs surface of boulder, for instance) will increase with respect to time.

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2 years ago

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Matt Perger

As I said above 🙂 Just an example

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2 years ago

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Édouard Fabi

Thanks, both of you. That explains why Mahlkonig always stick to flat burrs. I heard conicals are more consistant and durable, are those facts? Is there any advantages of having conical burrs? So far so good as of my F10. When you say the problems i’ll be having are to do with the machine, are you talking conicals in general or precisely the F10?

Thanks.

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2 years ago

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dsc

With current grinders you are going in blind as there’s no way to quickly check alignment and do corrections whilst the grinder is fully assembled. You have to remove the top burr carrier to tighten burr bolts and have access to both burrs and whilst you can use professional tools to align (or at least check) the bottom burr, the top burr and burr carrier remains a bit of a mystery, due to the following: 1) unknown machining tolerances on the burr carrier 2) unknown machining tolerances on the location of the threaded section in the body of the grinder… Read more »

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2 years ago

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Joe

Hi Matt,

I think you’ve got a missing word here?

“I don’t have any data to back them up, and I’m even sure they’re all true.” You’re sure they’re all true, are you sure? 🙂

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2 years ago

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tionico

MAP on the Baratza Encore is $129 US, which I think is about 110 Eur. That 150 EUR seems high. Ca ‘t directly access Euro mains specs from Bratza here in the US (220/50) but I can’t imagine prices the other side the Puddle being that much different.

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2 years ago

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Benny Söderman

I’am interested of alignment tool.

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2 years ago

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Matt Perger

I can send you some raw data if you want?

This question will also be somewhat answered in the paper being published by myself, hendon, maxwell and others!

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2 years ago

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AndyS

Matt, say we “define” fines as any particles smaller than 100 microns, and boulders as everything larger. Then what percentage of the ground coffee for a typical EK43 espresso shot is fines and what percentage is boulders?
One could try and integrate the area under the curve on the particle distribution graph you posted in the EK43 part 2 hustle. But since the x axis is logarithmic, it’s not as simple as it first appears.

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2 years ago

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Ben

I would love an EK43 alignment tool. I took mine apart once looking at the cleaning video by Mahlkoenig not realising I didn’t know how to align the burrs!

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2 years ago

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Eric Calderwood

I too would be interested in an EK43 alignment tool.

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2 years ago

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knudi68

I used pricespy, and the cheapest one in Norway was
1615 NOK

1615 Norwegian kroner =
182.44978 U.S. dollars

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2 years ago

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AndyS

Here is one of the EK43 particle size distribution graphs received from Matt, showing particle volume (a proxy for mass) but with a linear scale. I added an arbitrary “fines” line in red at 100 um. You can see that the fines make up a very small part of the overall mass.

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2 years ago

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AndyS

Re: “Fines are fine,” I’d like to propose some alternate explanations for what you’ve said here. It’s true (as you say) that all the coffee flavor contained in fines is almost instantly accessible to water. BUT the total MASS of the fines is very low compared to the mass of large particles – so even though the flavor in fines is easily available, there just ain’t much of it! How do we know this? Well bear in mind that particle size distribution graphs like the one Matt previously posted have a logarithmic x axis. This greatly exaggerates the small particle… Read more »

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2 years ago

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AndyS

I’d love raw data if available, thank you!

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2 years ago

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Troy Gardner

playing with that stuff here, agreed grind size and pack both are primary variables responsible for the matrix permeability, and nonlinear amount of water needed for preinfusion and extraction, with a definite sweet spot that is dependent on those two (as well as roast level, bean dryness). This makes sense thinking of it as a matrix like scaffolding, or suspension bridges with wind passing through it….the looser the pack the bigger gaps between structural coffee cellulose and increased permeability to things passing through it, and more water needed to span the gaps between fines/grounds, but at the extreme end if… Read more »

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2 years ago

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Kevin Douglas

Any links on aligning Ek burrs? Are they always set perfectly from factory? Thanks

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2 years ago

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David Viscardi

Hey Mat I have realised that espresso always taste best in the morning, once you’re dialled in. My guess is that it is due to the grinder and machine being cooled. In contrast I always find that espresso loses body, aroma and flavour once it gets busy and you are pumping a hundred coffees an hour for the next 8 hours. It tastes over extracted even if you keep to the recipe. what can we do? coarse up? change the dose? let it run quicker? honestly, I think it is impossible to keep consistency maintaining a specific recipe (dose/time/yield) through… Read more »

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2 years ago

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Stefan

Hi Matt! I have bought an EK43 what I thought with coffeeburrs. But it was Turkish burrs! Should I change to coffeeburrs instead? What are the differences between the burrs in the matter of taste and extraction. I’m brewing V60 and espresso and use both dark and light roasted coffeebeans.

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